The present invention relates to a new and improved construction of gear tooth flank testing apparatus and a method for testing tooth flanks of gears.
Generally speaking, the gear tooth flank testing apparatus of the present invention is of the type comprising a housing which can be erected upon a bed or the like of a gear cutting machine. Moveably arranged upon the housing is a measuring feeler by means of two cross-wire arranged carriages having associated drive and displacement path measuring devices. The measuring feeler can be moved along two coordinate axes which intersect the axis of the workpieces or gear to be tested. Additionally, there is provided a control and evaluation circuit for moving the measuring feeler along a tooth flank of the gear or workpiece and for the comparison of the actual positions of the measuring feeler with predetermined reference positions.
Under the expression "gear cutting machine" as used in conjunction with the present invention, there is to be understood any random machine suitable for processing gear-shaped workpieces or toothed segment-shaped workpieces, such as gear cutter or gear grinding machines, wherein there is afforded for such machines the typical possibility of rotating the workpiece slowly about its own axis in relation to a bed, a stand or the like provided at the machine.
The feature that the housing of the gear tooth flank testing apparatus can be erected upon the bed or the like of the gear cutting machine means that, on the one hand, not all components of the tooth flank testing machine must be absolutely erected upon the gear cutting machine, rather that the control and evaluation circuit can be mounted separately and at a random spacing from the gear cutting machine, and that on the other hand, the housing need not be erected continuously at one and the same gear cutting machine. Quite to the contrary, such housing can be selectively and alternately erected in each case at one of a number of gear cutting machines, in order to carry out gear tooth measurements at a test piece during such time as the same is chucked at the related gear cutting machine, so that following the measuring operation it can be further machined without having to again be centered.
A feature that the measuring feeler can be moved by means of two cross-wise arranged slides or carriages along two coordinates intersecting the axis of the test piece or gear, is not intended to preclude in any way that the measuring feeler can be moved by means of a third carriage or slide also along a third coordinate axis, in other words, throughout a spatial rectangular coordinate system. However, such additional possibility of movement generally only then is required when the gear tooth flank testing machine is not only used for testing a gear tooth flank profile, but also for testing the pitch of the tooth helix or angle of the tooth.
Under the term "actual positions" of the measuring feeler, there should be understood the actual positions which the measuring feeler assumes during the measurement, while under the term "reference positions", there should be understood, on the other hand, those positions which the measuring feeler would assume if the measured tooth flank were free of any faults.
Each testing operation consists of two procedures, namely the determination of an actual state and the comparison of the actual state with a reference state. A tooth flank testing apparatus therefore not only has to determine, for instance, the actual profile of a tooth flank, but rather must compare such with a reference profile. It is for this reason that it is not sufficient for testing gear flanks to use the heretofore known methods and apparatuses, such as for instance disclosed in German Patent Publication No. 2,654,839, which are intended to measure the contour of a workpiece which is totally unknown as concerns its dimensions, in two or more dimensions. The invention therefore starts with aa gear tooth flank testing machine of the previously mentioned species, in other words, a machine having a control and evaluation circuit for moving the measuring feeler along a tooth flank of the test piece or gear as well as for comparing the actual positions of the measuring feeler with predetermined reference positions. According to a known tooth flank testing machine of this species, as disclosed for instance in German Patent Publication No. 2,364,916 and the corresponding U.S. Pat. No. 4,166,323, which is not only suitable for testing tooth flank profiles, rather also for testing the tooth helix pitch angles, and therefore possesses a measuring feeler moveable along the three axes of a spatial coordinate system, the control and evaluation circuit is designed such that it moves the measuring feeler, during standstill of the test piece along a predetermined path corresponding to the reference profile or the reference pitch helix of the test piece, and records the thus arising deviations of the measuring feeler as faults. To control the measuring feeler according to this technique it is necessary that the entire path data of the measuring feeler not only previously be stored as to the coordinates of such path, but also that such path data be transposed, based upon the first measurement result, in a manner such that it corresponds to the previously not predeterminable spatial arrangement of the housing of the tooth flank testing machine in relation to the gear being tested or workpiece. For this purpose, there is required a considerable expenditure in computer capacity and programming.
There is also already known to the art a tooth flank testing apparatus as disclosed in U.S. Pat. No. 3,741,659, wherein the gear to be tested or workpiece is rotated by its own drive about its axis and the measuring feeler is not moved along a predetermined path, rather is guided, by means of servo motors, along the tooth flank which is scanned by the measuring feeler. The rotation of the tested gear constitutes the control magnitude for the entire course of the movement. The correlation of the actual data to the reference data, needed for testing the tooth flanks, presupposes, that, on the one hand, between the axis of the tested gear and the guides for the cross-wise arranged carriages or slides, carrying the measuring feeler, there exists a predetermined spatial correlation, and on the other hand, there is operatively associated with the rotary drive for the tested gear a measuring device. This measuring device is capable of extremely accurately indicating at any point in time, the angular rotational position of the tested gear. In the case of conventional gear cutting machines there is however neither present such measuring device nor does there exist a predetermined correlation between the axis of rotation of the tested gear and a housing of a gear tooth flank testing machine which can be erected only temporarily at the gear cutting machine.